1. Field of the Invention
This invention relates in general to the memory access priority control in MPEG (Motion Picture Experts Group) circuitry, and in particular to an adaptive-selection method for memory access priority control in an MPEG processor. More particularly, this invention relates to an adaptive-selection method for dynamic control of memory access priority in an MPEG processor for improving decompression performance by reducing unnecessary takeover of the system resource.
2. Description of the Related Art
As a result of advancements in fields including the digital signal processing technology, material science, as well as laser engineering, storage and retrieval of audio and video signals in digital format have become the selection of nature for high-fidelity sound and motion picture reproduction industry. In the broadcast of entertainment programs, there has been the similar trend of change toward digital format and away from the aging analog format that laid its technological basis several decades ago.
Due to the huge installation base of analog receiver equipment at the consumer end such as television sets and radio receivers, other than the last segment of signal transmission to the subscriber end is still implemented in the analog scheme. There has been the ever popular use of digital format when the program signal is manipulated or processed, either in the process of storage/retrieval or transmission. For example, satellites broadcast digital signals to ground stations, which then convert and relay the program signal in analog to the subscribers' houses via the cable network. There has even been several proposed standards for all-digital broadcast systems such as those incorporated with the widely expected High-Definition TV (HDTV). The above-mentioned trend of switching away from the analog toward the digital processing scheme is, based on what is currently available. The technology of digital storage and retrieval for audio and video signals is better than its analog counterpart and provides much better results. Digital processing provides virtually the only means for superior quality of sound and video reproduction in the cost-effective manner that human physical perception capabilities of both hearing and vision can demand.
Among the various digital signal compression/decompression schemes, MPEG standard, either MPEG-I or MPEG-II, emerges as one of the most promising and widely-accepted in the multimedia industry. At the signal decompression, namely, the reproduction end, like many others, the MPEG scheme relies on the use of digital signal processing (DSP) circuit elements to implement data retrieval for the playback of programs from a source that supplies signals containing compressed audio and video data. The source of compressed data for the MPEG processor circuitry in a playback device may be, for example, the latest members in the popular Compact Disc (CD) family of data storage formats that include the Video CD (VCD) or the Digital Video Disc (DVD). Or, the MPEG processor circuitry may also receive its compressed data signal source from a digital broadcast station.
To implement the audio and video signal reproduction utilizing compressed data fetched from signal sources in a multimedia application that employs the MPEG standard, dedicated digital electronic hardware circuitry known as MPEG processors must be used. These MPEG processors may be constructed utilizing digital circuitry elements built around digital signal processors and microprocessors that execute a firmware scheme for the implementation of the MPEG decompression operation. Memory resources are also used in the process of implementing the MPEG decompression. In fact, MPEG processors rely heavily on the use of memory subsystems as the multimedia data is being decompressed for program playback.
However, conventional hardware modules in the digital electronic circuitry that implements the MPEG standard of audio and video signal decompression employ a fixed memory access priority in a small and self-sustained firmware system. In such conventional MPEG systems, utilization of system resources can not be optimized to take full advantage of the supported bandwidth of the data bus that links the CPU, the DSP (digital signal processor), the memory and the supporting logic circuitry of the system together. As is familiar to persons skilled in the art of digital processing, unbalanced use of resources in a digital system can be translated directly into the waste of overall system power. Increase of the performance capabilities of many of the constituent parts in the system will be necessary. Such performance increase is necessary in order to achieve the same level of system processing capability as that which has well balanced use of resources. In other words, an MPEG system conducting unbalanced usage of resources (including the bus bandwidth) among all the constituent modules would require the use of either more powerful CPU, DSP, or other circuitry when compared to the one that has well-balanced system resource utilization.
In particular, in the case of MPEG decompression operation, if the memory access priority is fixed among all the functional modules in the MPEG processor, there would be a phenomenal wastes of memory bus bandwidth as the CPU is trapped in an endless scanning firmware loop. On the other hand, whenever any module in the MPEG processor requires access to resources over the system bus, it is frequently the situation that the bus is occupied. In this case, the requesting module has in a be put to waiting status. The result is that the system spends considerable time for the controlling CPU to execute its polling, while the DSP section of the system jams along the way trying to gain access to the bus for accessing data in the memory subsystem.